Sequential Processing of an Array Using Events

/* Created by raisch on 3/21/16. */

/*jshint node:true, bitwise:true, camelcase:false, curly:true, undef:false, unused:false, eqeqeq:true, shadow:true */

'use strict';

var assert = require('assert'),
    event = require('events');

/**
 * MOCK for penthouse
 * @param {object} opts
 * @property {string} opts.url
 * @param {function} cb
 */
var penthouse = function(opts, cb) {
  console.log('url: %s', opts.url);
  cb(null, 'RESULT FOR ' + opts.url);
};

var emitter = new event.EventEmitter();

/** MOCK - Container for URL records read from CSV file.
 *
 * @type {Array}
 */
var urls = [
  [null, null, 'url1'],
  [null, null, 'url2'],
  [null, null, 'url3']
];

/** Event handler to process a single URL
 *
 * @emits processUrl
 */
var onProcessUrl = function() {

  // always check your assumptions
  assert(Array.isArray(urls), 'urls must be an array');

  var urlRecord = urls.shift();

  if(urlRecord) {

    assert(Array.isArray(urlRecord), 'urlRecord must be an array');

    assert(urlRecord.length > 2, 'urlRecord must have at least three elements');

    penthouse(
        {
          url: urlRecord[2]
        },
        function(e, res) {
          if(e) {
            console.error('failed to process record %s: %s', urlRecord, e);
            return; // IMPORTANT! do not drop through to rest of func!
          }

          // do what you need with the result here
          console.log('RESULT: %s', res)

          if(urls.length === 0) { // ok, we're done
            console.log('completed processing URLs');
            return;
          }

          emitter.emit('processUrl');
        }
    );
  }
}

/**
 * processUrl event - triggers processing of next URL
 *
 * @event processUrl
 */
emitter.on('processUrl', onProcessUrl); // assign handler

// start...
emitter.emit('processUrl');